Controllable high voltage source having fast settling time

ABSTRACT

A high voltage d.c. stepping power supply for sampling a utilization device such as an electrostatic analyzer has a relatively fast settling time for voltage steps. The supply includes a waveform generator for deriving a low voltage staircase waveform that feeds a relatively long response time power supply deriving a high output voltage generally equal to a predetermined multiple of the input voltage. In the power supply, an a.c. voltage modulated by the staircase waveform is applied to a step-up transformer and thence to a voltage multiplier stack to form a high voltage, relatively poor replica of the input waveform at an intermediate output terminal. A constant d.c. source, applied to the input of the power supply, biases the voltage at the intermediate output terminal to be in excess of the predetermined multiple of the input voltage. A fast shunt regulator responsive to the input signal provides an output which is a faithful high voltage reproduction of the staircase waveform. The shunt regulator includes a solid state shunt device connected to the intermediate output terminal via a dropping resistor. The supply output is taken from the junction of the resistor and the shunt device.

Uni-ted States Patent Doong et a1.

[ CONTROLLABLE HIGH VOLTAGE SOURCE HAVING FAST SETTLING TIME [75] Inventors: Henry Doong, Beltsville; Mario H.

- Acuna, Bowie, both of Md.

[73] Assignee: The United States of America as represented by the Administration of the National Aeronautics and Space Administration, Washington, DC.

[22] Filed: Mar. 19, 1974 [21] Appl. No.: 452,761

Primary E.\'aminer-R. N. Envall, Jr. Attorney, Agent, or FirmRobert F. Kempf; Ronald F. Sandler; John R. Manning [111 3,869,659 [451 Mar. 4, 1975 [57] ABSTRACT A high voltage d.c. stepping power supply for sampling a utilization device such as an electrostatic analyzer has a relatively fast settling time for voltage steps. The supply includes a waveform generator for deriving a low voltage staircase waveform that feeds a relatively long response time power supply deriving a high output voltage generally equal to a predetermined multiple of the input voltage. In the power supply, an 21.0. voltage modulated by the staircase waveform is applied to a step-up transformer and thence to a voltage multiplier stack to forma high voltage, relatively poor replica of the input waveform at an intermediate output terminal. A constant d.c. source, applied to the input of the power supply, biases the voltage at the intermediate output terminal to be in excess of the predetermined multiple of the input voltage. A fast shunt regulator responsive to the input signal provides an output which is a faithful high voltage reproduction of'the staircase waveform. The shunt regulator includes a solid state shunt device connected to the intermediate output terminal via a dropping resisthe resistor and theshunt device.

16 Claims, 3Drawing Figures SOURCE 48 54 7 1 ELEcTRosmT l ANALYZER WA A- SOURCE PATENTED 4 7 womzow 0 0 CONT-ROLLABLE HIGH-VOLTAGE SOURCE HAVING FAST SETTLING TIME I ORIGIN OF THE INVENTION The invention describedherein was made by employeesof the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of royalties thereon or therefor.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION High voltage power supplies having a staircase output voltage waveform are used on board spacecraft as a desample the chargedparticle velocity distribution functions of a hot plasma viewed from the spacecraft. In-

such an application, particularly in conjunction with a fast spinning spacecraft, it is highly desirable that the. supply have both low power dissipation and a short settling time, on the order of 200 microseconds, for producing the staircase steps sufficiently fast to maximize spatial resolution and permit rapid precise measurement.

Prior art stepping power supplies with low power dissipation have generally been mechanized by modulating-an a.c. source with an input staircase low voltage waveform and applying the modulated a.c. to a step-up transformer followed by a voltage multiplier stack. These supplies, principally due to the characteristics of the voltage multiplier, have been unable to satisfy the aforementioned requirements for sampling a spacecraft born electrostatic analyzer. Prior art supplies of this type with low power dissipation consistent with a spacecraft environment have generally had settling times between voltage steps-on theorder of 20 milliseconds. For the case of fast spinning spacecraft, this settling time can be as much as 100 times too slow. It is estimated thatif the voltage multiplier of sucha supply were designed to meet the settling time requirement, the resultant power supply would have a power dissipation of about 50 times that desired.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION The stepping high voltage power supply of themesent invention, as in the prior art, comprises a waveform generator deriving a low voltage staircase waveform flectiori voltage source for electrostatic analyzers to which modulates an a.c. signal. The modulated a.c. signal is applied to a step-up transformer and voltage multiplier stack to form a high voltage unidirectional signal which is a predetermined multiple of said low voltage waveform.

In the present invention, in contradistinction to the prior art, the staircase waveform is biased with a dc. source so that the output high voltage of the multiplier is in excess of the predetermined multiple of said input signal. A shunt regulator rapidly responsive to said low voltage waveform includes shunt devices coupled to the voltage multiplier output via a dropping resistor across which is developed an output voltage equal to the predetermined multiple of the input waveform. For reliability, the shunt devices are solid state, comprising a plurality of transistors having emitter and collector electrodes connected in series to achieve the required voltage breakdown rating.

Because the capacitors of a voltage multiplier charge through forward biased diodes and discharge through back biased diodes, the output voltage of the multiplier can increase rather rapidly but can only decrease relatively slowly. Since the shunt regulator rapidly decreases the voltage of the multiplier, theresult is a controllable power supply having rapid response for either increasing or decreasing the output voltage.

Other objects and features of the present invention will become apparent upon perusal of the following detailed description of one embodiment of the present invention taken in conjunction with the appended drawmg.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical schematic of the stepping power supply of the present invention.

FIG. 2 is a logarithmic versus linear plot of input voltage to the FIG. 1 supply, as a function of time.

FIG. 3 is a logarithmic versus linear plot of output voltage of the FIG. 1 supply, as a function of time.

DETAILED DESCRIPTION OF THEDRAWING Referring to FIG. 1, the high voltage stepping power supply of the present invention includes a slow or long response time controllable power supply 12 having an input terminal 14 for receiving an input signal E (FIG. 2') derived by a staircase waveform generator 16. The

-output of generator 16 is a positive going, staircase waveform including a portion 18, which generally rises from a maximum negative voltage V (on the order of 5 volts) to zero volts in preferably 16 staircase steps 20 at varying amplitude, and a fly back portion 22 from zero volts to -V. 1

Waveform generator 16 comprises a clock source 24 which feeds a four stage binary counter 26 having a four bit parallel output 28 that is coupled to a four bit digital to analog converter 30 for deriving the voltage E coupled to terminal 14. Clock source 24 preferably has a frequency on the order of 50 Hertz to provide 20 millisecond spaced voltage steps 20 that occur synchro nously with pulses from the-clock.

As will become apparent, long response time power supply 12 derives a positive output voltage at its output '(gain) on the order of 300. As with prior art supplies the power supply 12 has a settling time onjthe order of milliseconds and has a tendency to follow, but does .not faithfully reproduce, the waveform of E at its output terminal 31. As will bebetterunderstood as the description proceeds, the present invention provides a faithful reproduction of the E waveform at terminal 52 byiconnecting dropping resistor 34 between termi- E is coupled to a virtual ground input terminal 36 of power supply 12 via an input resistor R connected connected between virtual ground input terminal 36 and output terminal 31 providing power supply 12, a negative voltage gain given by the ratio of R to'R Supply 12 is actually a d.c. to ac. to d.c. converter and includes amodulator 38 that is fed by the signal on inputterminal 36 and by the output of a high frequency sinusoidal oscillator 40, having a frequency typically on the order of 50 kilohertz. The output of modulator 38, a variable amplitude sinusoidal signal having an amplitude proportional to the d.c. signal on input terminal 36,is applied to a step-up transformer 42 to provide additional voltage gain. The a.c. output of step-up transformer 42 is applied to a conventional rectifying, voltage multiplier stack 43 comprising diodes 44 and capacitors'46. Voltage multiplier 43 derives a relatively high level, positive d.c. voltage that is supplied to outv put terminal 31;

To provide freedom for shunt regulator 32 to operate forpositive and negative d.c.. voltage variations, a negative d.c. source 48 is coupled to input terminal 36-via an input resistor 50 to bias the output voltage on termirial 31 to a voltage in-excess of the voltage Em times the gain of supply 12. Preferably, d.c. source 48 and resistor 50 are chosen to bias thevoltage on terminal 31. about 100 volts in excessof that given by the gain of staircase waveform E via an input resistor R conbetween terminals 14 and 36. A feedback resistor R is tors'62 so thateach transistor is not stressed above the g supply 12 times E Thus, in the absence of d.c. source 48, the output voltage on terminal 31 would range from 0. to* 1,500' volts; with d.c. source 48 chosen as indicated, the voltage on terminal 31 ranges from 100 to 1,600 volts.

The output voltage, E derived between terminal. 52 and ground, is applied to a utilization device such as an electrostatic analyzer 54of either the cylindrical or spherical type for sampling charged particle velocities of a hot plasma. While the output voltage of power supply 12 appearing at'terminal 31 has poor settling time in response to the steps 20 of E and has a positive d.c. bias due to source 48, B is a faithful reproduction of E times a gain on the order of 300, i.e., E ranges from 0 to 1,5 00 volts in 16 proportional staircase steps. This faithful reproduction at terminal 52' is achieved by pulling the voltage at terminal 31 down in response to E via dropping resistor 34 with the controllable shunt regulator 32 connected between terminal 51 and the negative terminal 53 of a positively grounded, low d.c.

voltage source 55, typically having a voltage of 5 volts Shunt regulator 32 is controlled by high gain, noninverting amplifier 58 via amplifier output line 60. Am-' plifier 58 is in a path external to the series path of supply 12 (between terminal 14 and 52) and receives the nected between-terminal 14 and a virtual ground input terminal 62 of the amplifier. Amplifier 58 also receives the stepping supply output voltage B as a feedback signal via resistor R connected between virtual ground input terminal 62 and output terminal 52. Shunt regulator 32 and amplifier 58 have a negative overall gain given by the ratio of R to R which is chosen to be the same as the ratio of R toR For high reliability purposes, shunt regulator 32 comprises all solid state elements. Because'of-the relatively high maximum voltage appearing at terminal52, i.e.,

about 1,500 volts, and because ,of the limited breakdown voltage of available solid state devices, shunt regulator 32 comprises a plurality of NPN transistors62 (a through f) shunted by zener diodes 68 (0 through f Preferably there are six transistors 62, each having collector and emitter electrodes 64 and 66 connected in'a series or totem pole aran eme tbetweenf e mi al? and the ne v minal 53 of d.c. source 55.--The six transistors 62 are progressively labeled 62a to 62f from terminal 52 to source 55. Each transistor 62 has a breakdown voltage on the'order of 400 volts. This arrangement permits the voltage B to be generally divided across the transisbreakdown voltage. v

The collector and emitter electrodes 64 and 66 of each transistor are shunted by a separate zener diode,

68a to 68f, having a zener voltage selected in the range of about 250 to 300 volts to fix the maximum voltage acrosseach transistor. The emitter electrode 66 and fier output line 60 via a separate diode 74 in series with a current limiting resistor 76. Diodes 74 are poled to conduct current from line 60 into the base electrodes 70, thereby isolating the base voltages of the various transistors 62. a 1

I Shunt regulator 32 is variably driven into conduction by the output of amplifier'58 to reduce the voltage at terminal 52 below that of terminal 31 in response to E To this end, current is conducted out of supply 12 through dropping resistor 34 into shunt regulator 32 and passes serially from terminal 52 through a group of the zener diodes68 and thence through a group of tra t sistors 62 to the -5 volt return terminal of source 55. For the purpose of discussion it is assumed that zener diodes 68'have a zener voltage of 250 volts and that the instantaneous voltage of B is 1,200 volts. Starting from terminal52, the first four zener-diodes 68a to 68d are in conduction providing a voltage across diodes 68a cally controlled by the output of amplifier 58 so it'has a collector-emitter voltage drop of approximately 200 volts and the latter being saturated and having a voltage drop approaching zero volts to produce the 1,200 volts from terminal 52 to ground. The first four transistors 1 68a to 68d are maintained'cut off because the emitter voltages established by the first four zener diodes are higher than the small base voltage established by ampli- Thus, for any instantaneous voltage E not more than one of transistors 62 is dynamically controlled by amplifier 58 while the transistors above the controlled transistor are cut off and the transistors below the controlled transistor are saturated. Each of the transistors 62 assumes control in different adjoining 250 volt ranges, whereby transistor 62f dynamically controls E between 0 and 250 volts, transistor 62e dynamically controls E between 250 volts and 500 volts, etc. The shunt regulator 32 is returned to the small negative voltage of source 55, rather than to ground, to enable a small saturation voltage of transistors 62 to be overcome so that E can be controlled in the neighborhood of zero volts.

What has been described is a completely solid state stepping power supply in which E a high voltage replica of E as shown in FIG. 3, has been obtained with a staircase portion 82 having settling times of 200 microseconds between steps 80, enabling rapid, precise sampling of electrostatic analyzer 54. Furthermore, the power supply 12, while capable of only slow discharge through back biased diodes 44, has the capability of a rapid charging because in that situation the diodes 44 are forward biased. This rapid charging ability provides a rising flyback portion 84 of E from O to 1,500 volts in about 2 milliseconds.

The invention has provided the combination of a controllable power supply having a relatively fast response only for increasing voltage and a shunt regulator 32 having a fast response for decreasing voltage. The provision of control to both power supply 12 and shunt regulator 32 allows the maximum voltage across the dropping resistor 34 to be kept rather small, about 100 volts, resulting in low power dissipation. Since the electrostatic analyzer 54 represents substantially an open circuit enabling resistor 34 to be several megohms, the power dissipationin resistor 34 is less than about milliwatts.

Having described in detail a preferred embodiment of. the invention, it should be apparentthat numerous modifications may be made to the embodiment within the spirit and scope of, the invention. Hence, it is intended that the detailed description be considered as illustrative of the concept of the invention and'not in a limiting sense.

What is claimed is:

1. A controllable high voltage source having a relatively fast response to a low voltage input signal source with a predetermined gain comprising:

a pair of input terminals for said input signal source;

a pair of output terminals for high voltage output;

a relatively long response time controllable high voltage source coupled between said input and output terminals, said long response time source having said predetermined gain;

means for do. biasing said long response time controllable voltage source to have an output voltage in excess of the input signal times said gain; and fast response time shunt regulator means coupled across said output terminals responsive to said input signal at said input terminals for reducing the output voltage across said output terminals to said gain times said input signal. 2. The apparatus of claim 1 wherein said long response time source includes a rectifying voltage multi-' plier responsive to an a.c. source and means for conlong response time source has a relatively fast response for increasing said output voltage and a relatively slow response for decreasing said output voltage.

4. The apparatus of claim 2 wherein said output voltage has only one polarity and further including a source of relatively low dc. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.

5. The apparatus of claim 3 wherein said output voltage has only one polarity and further including a source of relatively low dc. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.

6. A high voltage stepping power supply having relatively fast settling time for voltage steps comprising:

a digital clock source;

means for deriving a low voltage staircase analog input voltage signal having steps synchronous with said clock source;

a pair of output terminals;

a relatively long response time controllable high voltage source responsive to said input voltage signal, said high voltage source having a predetermined gain, said high voltage source being coupled to said output terminals, means for d.c. biasing said high voltage source to have an output voltage in excess of said analog voltage times said gain; and

fast response time shunt regulator means responsive to said input signal coupled across said output terminals for reducing the output voltage at said output terminals to said gain times said input signal.

7. The apparatus of claim 6 wherein said high voltage source includes a rectifying voltage multiplier responsive to an a.c. source and means for controlling the amplitude of said a.c. source in response to said input sig- 8. The apparatus of claim 6 wherein said high voltage source has a relatively" fast response for increasing said output voltage and a relatively slow response for decreasing said output voltage.

9. The apparatus of claim 7 wherein said output voltage has only one polarity and further including a source of relatively low dc. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.

10. The apparatus of claim 8 wherein said output voltage has only one polarity and further including a source of relatively low dc. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.

11. A high voltage source having an output terminal for developing a high voltage capable of following relatively rapid variations of a relatively low voltage input source comprising an input terminal responsive to the input source, a series path between the input and output terminals said path including a dc. to a.c. to d.c.

7- converter connected to be responsive to the voltage at the input terminal forderiving a high voltage output having a tendency to follow-the variations, a variable impedance shunt path having substantially only resistive components connected across the output terminal, and means external to the first path responsive to the voltage at the input terminal for controlling the impedance of the shunt path.

12. The source of claim 11 wherein the converter includes a voltage multiplier having diodes and capacitors.

13. The source of claim 12 further including a resistor series connected between the output of the converter and the output terminal, said means for controlling the impedance of the shunt path including a noninverting d.c. amplifier, said amplifier having an input terminal connected to be responsive to theinput source and a feedback resistor connected between the output terminal and the'amplifier input terminal.

14. The source of claim 13 wherein the shunt impedance includes plural series connected variable impedance elements, each of said elements including means for enabling a (a) predetermined, finite voltage, (b) a substantially zero voltage and (c) dynamic voltage to be developed across them in response to the voltage at the output terminal, and means for dynamically con-- trolling the voltage. developed across only'one of the elements at a time in response to an output voltage of the amplifier. y

15. The source of claim 14 further including a first input resistor between the relatively low voltage input terminal and the amplifier-input terminal, a second input resistor between the relatively low voltage input terminal and an input terminal of the'converter, and another feedback resistor between the converter output and the'converter input terminals, the ratio of the input resistor to the feedback resistor for the amplifier being substantially equal to that for the converter so that the gain of the series path including the converter andv the path including the amplifier are substantially the same.

, ance elements, each of said elements including means yes for enabling a (a) predetermined, finite voltage, (b) a substantially zero voltage and (c).dynamic voltage to be developed across them in response to the voltage at the output terminal, and means for dynamically controlling the voltage developed across only one of the elementsat a time in response to an output voltage of the amplifier means for controlling the shunt path impedance. 

1. A controllable high voltage source having a relatively fast response to a low voltage input signal source with a predetermined gain comprising: a pair of input terminals for said input signal source; a pair of output terminals for high voltage output; a relatively long response time controllable high voltage source coupled between said input and output terminals, said long response time source having said predetermined gain; means for d.c. biasing said long response time controllable voltage source to have an output voltage in excess of the input signal times said gain; and fast response time shunt regulator means coupled across said output terminals responsive to said input signal at said input terminals for reducing the output voltage across said output terminals to said gain times said input signal.
 2. The apparatus of claim 1 wherein said long response time source includes a rectifying voltage multiplier responsive to an a.c. source and means for controlling the amplitude of said a.c. source in response to said input signal.
 3. The apparatus of claim 1 wherein said relatively long response time source has a relatively fast response for increasing said output voltage and a relatively slow response for decreasing said output voltage.
 4. The apparatus of claim 2 wherein said output voltage has only one polarity and further including a source of relatively low d.c. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.
 5. The apparatus of claim 3 wherein said output voltage has only one polarity and further including a source of relatively low D.c. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.
 6. A high voltage stepping power supply having relatively fast settling time for voltage steps comprising: a digital clock source; means for deriving a low voltage staircase analog input voltage signal having steps synchronous with said clock source; a pair of output terminals; a relatively long response time controllable high voltage source responsive to said input voltage signal, said high voltage source having a predetermined gain, said high voltage source being coupled to said output terminals, means for d.c. biasing said high voltage source to have an output voltage in excess of said analog voltage times said gain; and fast response time shunt regulator means responsive to said input signal coupled across said output terminals for reducing the output voltage at said output terminals to said gain times said input signal.
 7. The apparatus of claim 6 wherein said high voltage source includes a rectifying voltage multiplier responsive to an a.c. source and means for controlling the amplitude of said a.c. source in response to said input signal.
 8. The apparatus of claim 6 wherein said high voltage source has a relatively fast response for increasing said output voltage and a relatively slow response for decreasing said output voltage.
 9. The apparatus of claim 7 wherein said output voltage has only one polarity and further including a source of relatively low d.c. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.
 10. The apparatus of claim 8 wherein said output voltage has only one polarity and further including a source of relatively low d.c. voltage opposite in polarity to said output voltage, said shunt regulator means including a plurality of transistors having emitter and collector electrodes connected in series between one of said output terminals and said low voltage source.
 11. A high voltage source having an output terminal for developing a high voltage capable of following relatively rapid variations of a relatively low voltage input source comprising an input terminal responsive to the input source, a series path between the input and output terminals said path including a d.c. to a.c. to d.c. converter connected to be responsive to the voltage at the input terminal for deriving a high voltage output having a tendency to follow the variations, a variable impedance shunt path having substantially only resistive components connected across the output terminal, and means external to the first path responsive to the voltage at the input terminal for controlling the impedance of the shunt path.
 12. The source of claim 11 wherein the converter includes a voltage multiplier having diodes and capacitors.
 13. The source of claim 12 further including a resistor series connected between the output of the converter and the output terminal, said means for controlling the impedance of the shunt path including a non-inverting d.c. amplifier, said amplifier having an input terminal connected to be responsive to the input source and a feedback resistor connected between the output terminal and the amplifier input terminal.
 14. The source of claim 13 wherein the shunt impedance includes plural series connected variable impedance elements, each of said elements including means for enabling a (a) predetermined, finite voltage, (b) a substantially zero voltage and (c) dynamic voltage to be developed across them in response to the voltage at the output terminal, and means for dynamically controlling the voltage developed across only one of the elements at a time in response to an output voltage of the amplifier.
 15. The source of claim 14 further including a first input resistor between the relatively low voltage input terminal and the amplifier input terminal, a second input resistor between the relatively low voltage input terminal and an input terminal of the converter, and another feedback resistor between the converter output and the converter input terminals, the ratio of the input resistor to the feedback resistor for the amplifier being substantially equal to that for the converter so that the gain of the series path including the converter and the path including the amplifier are substantially the same.
 16. The source of claim 12 wherein the shunt impedance includes plural series connected variable impedance elements, each of said elements including means for enabling a (a) predetermined, finite voltage, (b) a substantially zero voltage and (c) dynamic voltage to be developed across them in response to the voltage at the output terminal, and means for dynamically controlling the voltage developed across only one of the elements at a time in response to an output voltage of the amplifier means for controlling the shunt path impedance. 